The present invention refers to an automatic defrost system of the evaporator of refrigerating devices, to be applied to refrigerators and freezers, in which the evaporator may be provided isolated from the refrigeration compartment during defrost operations, particularly in the xe2x80x9cno frostxe2x80x9d type refrigerators.
The refrigerator constructions provided with a freezing compartment of the xe2x80x9cno frostxe2x80x9d type usually present automatic defrost of the evaporator. Ice formation in the evaporator occurs due to the existence of humidity in this region, resulting from the air returning from any of the refrigerating and freezing compartments. In order that defrost may occur, the control system of these devices instructs, periodically, the actuation of a heat source, such as a resistor.
In this condition, the compressor is automatically turned off and an electric resistance, which is provided adjacent to the evaporator, is energized by a current, whose intensity is known and predetermined as a function of the amount of heat needed to eliminate only the undesired ice layer formed in the evaporator, without impairing the refrigeration of the internal environment of the cabinet.
The energization of the resistance promotes a superficial heating of the evaporator plate, gradually melting all the ice formed on the plate, which ice, when liquefied, is drained outwardly from the refrigeration environment.
The ice acts as a thermal insulating element, making difficult the heat transfer between the evaporator and the air returning from the refrigerating and freezing compartments, resulting in a degradation of the refrigeration system characterized by an increase of energy consumption, since the refrigeration system has to work more to comply with the operational conditions and/or the increase of the internal temperature of the refrigeration environments.
Thus, the localized ice formation in the evaporator requires a periodic defrost operation. With this localized ice formation, such defrost operation has to be executed more frequently, increasing energy consumption.
Thus, it is an objective of the present invention to provide an automatic defrost system for refrigerators and freezers, which promotes the automatic defrost of said equipments with minimum energetic consumption. Another objective of the present invention is to provide a defrost system for refrigerators and freezers, such as cited above, in which the consumed energy for promoting the automatic defrost of said equipments is obtained from the dissipation of energy of said equipments.
These and other objectives are achieved by an automatic defrost system for a refrigerating device, whose cabinet comprises a freezing compartment and a refrigerating compartment, a refrigeration circuit including a condenser and an evaporator, and a refrigeration forced air circuit comprising said compartments and the evaporator, further comprising a defrost air circuit having: a first circuit portion, through which flows a certain defrost airflow; a second circuit portion receiving the defrost airflow from the first circuit portion and positioned adjacent to the condenser, in order to exchange heat with the latter and heat the defrost airflow; a third circuit portion, which selectively receives, from the second circuit portion, the defrost airflow, and which is positioned adjacent to the evaporator, so as to be in direct contact with the latter and heat it when the refrigerating device is under a defrost condition, and conducting the defrost airflow to the first circuit portion; and a valve means, which selectively permits the passage of the defrost airflow from the second circuit portion to the third circuit portion, upon occurrence of a certain ice formation condition in the evaporator, and blocks said passage of defrost airflow, upon completion of the defrost in the evaporator.